lulbtiu 0f 

(Hty? Hmu?rmtg of Minmnotn 

MINNESOTA SCHOOL OF MINES 
EXPERIMENT STATION 

WILLIAM R. APPLEBY, Director 
BULLETIN No. 6 


A NEW MACHINE FOR CONCENTRATING 
MINNESOTA WASH ORES 

BY 

EDWARD W. DAVIS 



VOL. XXII NO. 56 DEC. 16 1919 
MINNEAPOLIS 


Entered as second-class matter at the Post Office at Minneapolis, Minnesota 
Under Act of Congress, March 3, 1879 

Acceptance for mailing at special rate of postage provided for in section 1103, 
Act of October 3, 1917, authorized July 12, 1918 










Sulbtttt of 

®ljp Iniumity nf MxmtmU 

MINNESOTA SCHOOL OF MINES 
EXPERIMENT STATION 

WILLIAM R. APPLEBY, Director 
BULLETIN No. 6 


A NEW MACHINE FOR CONCENTRATING 
MINNESOTA WASH ORES 

BY 

EDWARD W. DAVIS 



VOL. XXII NO. 56 DEC. 16 1919 
MINNEAPOLIS 


Entered as second-class matter at the Post Office at Minneapolis, Minnesota 
Under Act of Congress, March 3, 1879 

Acceptance for mailing at special rate of postage provided for in section 1103, 
Act of October 3, 1917, authorized July 12, 1918 






Copyright 1919 

BY THE 

University of Minnesota 


% i 


* 


©Cl A563S76 


4 


FES lb 1920 


| 


A NEW MACHINE FOR CONCENTRATING 
MINNESOTA WASH ORES 


It is the purpose of this publication to answer in a definite and 
convenient way many inquiries received from the mining men of the 
Minnesota iron ranges concerning the new type of ore-washing machine 
lately developed at the School of Mines Experiment Station, and to 
point out the possibilities of its usefulness. 

During the past year the Mines Experiment Station has received 
several requests from mine owners and operators for information 
regarding some means of washing ore in a moderately priced plant of 
a more or less portable nature. With the hope of answering such 
requests, the Station undertook a series of experiments leading toward 
the development of a new machine for washing ores. The result of 
the experimental work conducted by E. W. Davis was the develop¬ 
ment of a machine which has been called the Dorr Ore Washer. 

A brief outline of ore washing in Minnesota and the characteristics 
of typical wash ores are presented in order to give the reader a clear 
idea of the relation of this new machine to the work of beneficiating 
low-grade iron ores. 

The washing of Minnesota iron ores began in 1907 when the 
Oliver Iron Mining Company made the first shipment of concen¬ 
trated iron ore from its experimental plant near Trout Lake, Minne¬ 
sota. In 1910 the first shipment of washed ore was made from the 
present concentrating plant at Coleraine. This plant operated so 
successfully that other mining people became interested in the wash¬ 
ing process. At the present time there are 17 washing plants in the 
state, capable of producing annually approximately 10,000,000 tons 
of washed ore. These plants are similar in general design, differing 
only in detail. The description of these plants, their methods of 
operation, and the ores that are treated appear in current publica¬ 
tions.* All of the plants are built on the unit plan, and each unit 
will produce from 50 to 200 tons of concentrate per hour, depending 

• J. U. Sebenius, Wash ores of the western Mesabi range and the Coleraine concentrating 
plant. Lake Superior Mining Institute 18:15,5-86. 1913. 

Benedict Crowell, Concentrating at the Madrid mine. Ibid. 18:129-32. 1913. 

H. H. Stock, Concentration of Mesabi ores. Mines and Minerals 29:97-98. 1908. 

-Iron ore concentration in Minnesota. Metallurgical and Chemical Engineering 10:717-19. 

1912. 

-Plants for washing lean iron ores. Engineering News 68:449. 1912. 

P. A. Kennedy, Iron ore washing plants on the Mesabi range. Engineering and Mining 
Journal April 19, 1919. 

-Iron ore washing plants. Bulletin no. 1807, A. Allis-Chalmers Mnfg. Co. 





2 


A MACHINE FOR CONCENTRATING WASH ORES 


upon the nature of the ore and the grade of the product desired. A 
one-half unit plant of .standard construction consisting of a large 
washing trommel, a 25-foot log-washer, two 18-foot log-washers, 
together with the necessary table equipment, will cost from $75,000 
to $125,000 and will produce washed ore at a cost of approximately 
25_cents per ton. 

i The following screen analysis of a crude ore best describes the 
typical wash ore. 


Ore No. 441 Screen analysis of crude ore 

Size % by weight % Fe 

On 1.050-inch. 7.65 59.36 

On .742-inch. 6.73 59.36 

On .371-inch. 17.12 58.71 

On 4-mesh. 15.63 59.26 

On 8-mesh. 9.39 58.80 

On 14-mesh. 5.76 57.33 

On 28-mesh. 3.85 55.21 

On 48-mesh. 2.97 52.44 

On 65-mesh. 1.40 48.57 

On 100-mesb. 1.40 41.57 

Through 100-mesh. 28.10 13.46 

Unsized. 100.00 45.30 


The important facts shown in the screen analysis are (1) the 
amount of low-grade material passing a 100-mesh screen and (2) the 
high iron content of the material coarser than 100-mesh. The con¬ 
centrating process consists in washing out the fine low-grade material 
from the ore, thereby producing a high-grade concentrate. Such an 
ore as represented by the above screen analysis can be washed and will 
produce a concentrate assaying 58 per cent iron, representing 68 per 
cent of the weight of the original material and containing 87 per cent 
of the total iron. 

There is a very large amount of wash ore in Minnesota but it does 
not always occur in large ore bodies. It also frequently happens that 
there is a certain amount of coarse silica in the ore material that can 
not be washed out by the standard concentrating process. Such ore 
produces a low-grade concentrate which is of doubtful value. In 
cases where the body of wash ore is small or the concentrate which 
may be produced is low grade, it is often impossible to realize a profit 
after paying the cost of installing and operating a standard washing 
plant. 

The Dorr Ore Washer is a single machine containing the entire 
concentrating mechanism of the washing plant. In addition to this 
machine, it is necessary to provide only a bin from which the ore 
may be fed to the machine and a small pocket in which the concen¬ 
trate may be stored during the shifting of the cars. The plant can be 














A MACHINE FOR CONCENTRATING WASH ORES 


3 


built at a moderate price and will require less water and less power 
than a standard washing plant. 

The two accompanying photographs and the drawing show the 
machine as it appears in the laboratory. A bi-size Dorr Classifier 
is used as the body of the machine and a bt by j/^-inch rectangular 
mesh cylindrical screen is mounted in the rear of the tank in such a 
manner that the lower portion of the screen is submerged in the water 
in the classifier tank. The ore enters through the feed spout and falls 
directly into the revolving screen where the coarse material is com¬ 
pletely washed before being discharged over the rear end of the classi¬ 
fier as a coarse concentrate. The material that passes through the 
openings in the screen enters the tank of the classifier, where the 
coarser and heavier particles settle to the bottom and are raked out 
and discharged at the upper end of the classifier as fine concentrates. 
The finer and lighter particles are kept in suspension by the rakes and 
are discharged as tailing with the excess water admitted as a surface 
spray at the upper end of the tank. 

The speed of the trommel or screen is so adjusted that the ore 
within it is subjected to a cascading action similar to the action of 
the material in a ball mill. The lumps of ore are carried out of the 
water on the side of the trommel, from which position they fall or 
cascade back into the water. ' This action continues until the ore 
finally reaches the lower end of the trommel where a discharge scoop, 
similar to the feed scoop of a ball mill, picks up the coarse washed 
ore and discharges it, comparatively free from water, from the 
machine. In order to carry a considerable charge of material in the 
trommel at all times, the slope is made very small. This has the effect 
of causing the particles of ore to rub together and to wear ofi the soft 
clay or sand. The presence of large lumps of ore in the trommel is 
quite desirable in order to increase this abrasive action, and no pre¬ 
liminary screening or sizing of the ore is found necessary. By placing 
a coarse screen or grate across the trommel near the discharge end, the 
coarse material may be retained in the trommel, thereby greatly 
increasing the abrasion of the coarse ore. This is particularly desir¬ 
able when the ore contains a large amount of paint rock or partially 
disintegrated silica. The abrasive effect may be further increased, if 
necessary, by the addition of steel balls. The power required to 
operate a trommel of any given dimension is proportional to the 
speed and the load of material that it carries. The trommel, therefore, 
may be considered as a modification of a ball mill and by slight 
alterations may be made to operate as much like a ball mill as is 
desired. 




















Drive Pulk 



DORR ORE WASHER 






















































A MACHINE FOR CONCENTRATING WASH ORES 


7 


The Dorr Classifier which is used as the tank is a well-known 
standard machine and has been in successful use many years. It is 
simple, t'ugged, efficient, and requires a minimum amount of attention, 
repairs, and power. The operation of the rakes may be described as 
similar to the actions of a man with a hoe, raking material out of a 
pool of water and up a slight incline. The hoe, or rake, as it is called, 
is made of two channel irons running the length of the machine. 
Across the underside of the two channel irons, angle irons are riveted. 
The angle irons are spaced 4 inches apart, thus providing a great 
number of these hoes in the length of the washer. The cycle of opera¬ 
tion consists in dropping the big rake into the material that has settled 
to the bottom of the classifier, moving the rake forward 6 inches 
together with its load of ore, raising the rake out of the ore, moving it 
backward to the original position, and dropping it into the ore again. 
This cyclic motion is produced by cams and bell cranks, all located 
near the upper end of the machine and well above the water line. All 
of the parts are slow moving, and records show that maintenance costs 
on machines handling as much as 100 tons of ore per hour are excep¬ 
tionally small. This can be explained by the fact that a machine 
raking out 1 ton of ore per minute requires less than 5 horse power 
for operation. 

The machine as built and tested in the laboratory of the Experi¬ 
ment Station is 8 feet long and 2j/£ feet wide. The trommel is 1J4 
feet in diameter and 3 feet long. This experimental plant is compara¬ 
tively small, as the full-sized Dorr Classifier is 273^ feet long and 
6 feet wide. The trommel with which the full-sized machine will be 
equipped will be 4 feet in diameter and 10 feet long. It will be made 
of 3/g-inch steel plate punched with round holes x /i inch in diameter 
spaced 1 inch between centers. 

The above brief description will give some idea of the construction 
and method of operation of the new ore-washing machine. It would 
appear from the viewpoint of ruggedness of construction and simplicity 
of operation, and from the result of many tests, that the machine 
would be readily adapted to the process of washing low-grade iron 
ores. The metallurgical results on testing this machine are, perhaps, 
best shown in a report that was prepared for and is herewith published 
through the courtesy of Mr. Clement Quinn of Duluth. The sample 
of ore which he submitted to the Mines Experiment Station was 
taken from the old Pearson mine near Nashwauk, and as shown by the 
screen analysis is a fairly representative wash ore. Many other tests 
have been made on the machine with a great variety of ores producing 
as satisfactory results, but this test has been selected as being the 
most comprehensive. 


Slip Uniuprsitg nf HHirntpaota 

iHtunrsota of HittrB 

minn^apoltfi 

OFFICE OF THE EXPERIMENT STATION 


August 30, 1919 


Mr. C. K. Quinn , 

Duluth , Minnesota. 

Dear Sir: Attached hereto is a copy of our report covering the 
work done on the sample of iron ore which you submitted from the 
Pearson Mine. 

As you will notice we have gone into the question of concentrating 
this material by use of the Dorr Classifier very completely. I trust 
that the results will be of value to you. 

Very truly yours, 

Signed: E. W. Davis, 
Supt. Mines Experiment Station 


EWD-G 

Copy to: Dorr Company 
E. P. Scallon. 


OBJECT 


The objects of this test were: 

1. To determine the grade of concentrate that could be made by 
treating the ore from the Pearson mine on the Dorr Ore Washer under 
various operating conditions, and, 

2. To compare the results secured by use of the Dorr Ore Washer 
with those secured in standard log-washing treatment. 

DESCRIPTION OF SAMPLE 

Mesabi range ore bodies are said to have been formed by the con¬ 
centration of iron and removal of silica in the original iron formation 
by percolating waters. In ore bodies of the so-called washable type, 
these processes of natural concentration have not been carried to com¬ 
pletion, for altho the iron is generally segregated into bands of fairly 
high-grade hematite, much of the silica still remains. The silica 
occurs largely in soft, more or less disintegrated bands, which during 
the mining and ore-dressing operations break down into very fine 
sand. 

The sample of this type of material obtained from the Pearson 
mine at Nashwauk, Minnesota, consisted of 226 bags weighing in all 
about 11 tons. A screen analysis of this sample showed 23 per cent 
by weight to be finer than 100 mesh, and this fine material carried 
only 27 per cent iron. The medium and coarse-size products were all 
of quite high iron content with the exception of the material coarser 
than 1 inch. In this size a small amount of coarse rock was present, 
causing a decrease in the iron assay. A noticeable characteristic of 
this ore was the small percentage of coarse lumps present. All of the 
material passed a 4-inch grizzly and only 7 per cent were held on a 
1-inch screen. 


METHOD OF TREATMENT 

The material after careful sampling was divided into 10 approx¬ 
imately equal portions. Each portion was heated separately in the 
Dorr Ore Washer. This machine was constructed at the Experi¬ 
ment Station as the result of an investigation having for its object 
the design of a simple and inexpensive plant for concentrating the 
Mesabi wash ores. The machine consists of a simplex Dorr Classi¬ 
fier, in the rear end of which is mounted a revolving trommel, the lower 
one fourth of which is submerged in the water in the tank of the classi¬ 
fier. In the lower end of the trommel is mounted a discharge scoop 


10 


A MACHINE FOR CONCENTRATING WASH ORES 


much like the feed scoop on a ball mill, which removes the material 
from the inside of the trommel and discharges it over the tail-board 
of the classifier in a comparatively dry condition. This trommel 
revolves at a speed sufficient to cause great agitation of the material 
within it. The ore is carried up on the side of the revolving trommel, 
from which it cascades back into the water. This cycle is repeated 
over and over until the lumps of ore reach the lower end of the trom¬ 
mel, where they are discharged by the feed scoop. The material which 
passes through the openings in the trommel settles into the classi¬ 
fying compartment of the machine. The heavier particles settle to 
the bottom and are raked out and delivered as a comparatively dry 
concentrate. The lighter particles overflow with the excess of water 
as tailing. 

In this test the ore was fed through a feed spout at a predeter¬ 
mined feed rate into the revolving trommel having rectangular open¬ 
ings M by J /2 inch. The oversize from this trommel was discharged 
as finished concentrate and the undersize passed into the classify¬ 
ing compartment of the machine. The heavier and coarser parti¬ 
cles settled to the bottom of the classifier and were raked out as 
finished concentrate, while the finer and lighter particles were carried 
over the overflow lip and discharged as tailing. 

The tailing was delivered into a settling cone from which the 
excess water and slime overflowed, leaving a thickened spigot prod¬ 
uct for feed to the oscillating tables. This thickened product was 
passed over a table and divided into concentrate and tailing. 

Weights were taken on the crude ore and on the concentrated 
products. The tailing from the Dorr Ore Washer and the final plant 
tailing were sampled throughout each test. 

DATA AND RESULTS 

The results of the various tests made on this sample of ore are 
given in the following tables. All recoveries are computed from 
dry weights and all analyses were made on samples dried at 212 0 F. 
Each test was made under different operating conditions. 

The variables that were considered were: 

1. Speed of rakes in strokes per minute. 

2. Water rate in tons per hour. 

3. Feed rate, tons per hour. 

4. Feed rate and water rate, i.e., the tons of water per ton of ore 
were kept constant but the feed rate of ore was varied. 

The results previously secured on this ore by use of the log- 
washer are included in this report for the purpose of comparison. 


A MACHINE FOR CONCENTRATING WASH ORES 


11 


The following data include in detail the results secured on each 
test as well as a general summary of the results secured on all of the 
tests. 


Ore No. 475 


SCREEN ANALYSIS OF CRUDE ORE 


Crude unsized. 
+ 1.050-inch 

+ . 742-inch 

+ .371-inch 

+ 4-mesh.. . . 
+ 8-mesh.. . . 
+ 14-mesh.. . . 
-f- 28-mesh.. . . 
-f- 48-mesh.. . . 
+ 100-mesh.. . . 
-(-200-mesh.. . . 
— 200-mesh.. . . 


% by 
weight 

%Fe 

100.00 

48.74 

7.00 

49.50 

3.24 

56.25 

13.50 

58.95 

12.27 

58.58 

9.30 

56.55 

7.83 

52.20 

4.52 

54.45 

8.66 

54.00 

10.42 

50.55 

9.83 

38.25 

13.43 

20.85 














Ore No. 475 
Test No. 3 


CONDITIONS OF TEST ON DORR ORE WASHER 

Water rate, 5.2 tons per hr. 

Feed rate, 1.0 tons per hr. 

Rake speed, 38 strokes per min. 



% by 


% Fe by 


weight 

% Fe 

weight 

Feed. 

. 100.00 

48.74 

100.00 

Screen oversize.■ . . . 

. 28.51 

58.48 

34. 19 

Rake concentrate. 

. 45.84 

56.82 

53.43 

Total coarse concentrate. 

. 74.35 

57.46 

87.62 

Dorr overflow. 

. 25.65 

23.51 

12.38 

Table concentrate. 

. 2.28 

61.05 

2.85 

Total concentrate. 

. 76.63 

57.56 

90.46 

Final tailing. 

. 23.37 

19.86 

9.54 


SCREEN ANALYSES 

Dorr Concentrate Dorr Overflow 





(% solids=4. 

75) 


% by 

% Fe 

% by 

%Fe 


weight 


weight 


+ .3 71-inch. 

. 38.35 

58.48 



+ 4-mesh. 

. 8.06 

60.60 



+ 8-mesh. 

. 10.67 

59.10 



+ 14-mesh. 

. 7.64 

56.25 



+ 28-mesh. 

. 7.05 

55.73 



+ 48-mesh. 

. 11.14 

56.18 



+ 65-mesh. 

. 4.83 

54.38 

.65 

25.42 

-flOO-mesh. 

. 6.31 

53.78 

11.11 

24.90 

-t-200-mesh. 

. 4.83 

58.28 

37.25 

24.52 

— 200-mesh. 

. 1.12 

46.43 

50.99 

22.42 

Unsized. 

. 100.00 

57.46 

100.00 

23.70 


12 





















Ore No. 475 
Test No. 2 


CONDITIONS OF TEST ON DORR ORE WASHER 

Water rate, 5.2 tons per hr. 

Feedrate, 1.0 tons per hr. 

Rake speed, 30 strokes per min. 


Feed.. 

Screen oversize. 

Rake concentrate. 

Total coarse concentrate 

Dorr overflow. 

Table concentrate. 

Total concentrate. 

Final tailing. 


% by 
weight 

%Fe 

% Fe by 
weight 

100.00 

48.74 

100.00 

25.36 

58.84 

30.61 

51.26 

56.51 

59.43 

76.62 

57.28 

90.04 

23.38 

20.76 

9.96 

1.48 

59.63 

1.81 

78.09 

57.33 

91.85 

21.91 

18.14 

8.15 


SCREEN ANALYSES 

Dorr Concentrate Dorr Overflow 





(% solids=4. 

,48) 


% bv 

% Fe 

% by 

% Fe 


weight 


weight 


-f- .3 71-inch. 

. 33.10 

58.84 



4- 4-mesh. 

. 10.44 

60.83 



4- 8-mesh. 

. 10.73 

59 10 



j- 14-mesh. 

. 8.66 

57.08 



f 28-mesh. 

. 6.09 

56.33 



4- 48-mesh. 

. 10.64 

56.33 



-f 65-mesh. 

. 5.33 

54.53 



-f 100-mesh. 

. 6.27 

53.10 

4 09 

25.58 

-f200-mesh. 

. 6.84 

52.13 

33.92 

19.58 

— 200-mesh. 

. 1.90 

49.20 

61 .99 

21 08 

Unsized. 

. 100.00 

57.28 

100 00 

20.76 


13 





















Ore No. 475 
Test No. 3 


CONDITIONS OF TEST ON DORR ORE WASHER 

Water rate, 5.2 tons per hr. 

Feed rate, 2.0 tons per hr. 

Rake speed, 30 strokes per min. 



% by 

% Fe 

% Fe by 


weight 


weight 

Feed. 

. 100.00 

48.74 

100.00 

Screen oversize. 

. 27.85 

58.31 

33.32 

Rake concentrate. 

. 49.68 

56.26 

57.33 

Total coarse concentrate. 

. 77.53 

57.00 

90.65 

Dorr overflow. 

. 22.47 

20.28 

9.35 

Table concentrate. 

. 1.77 

54.08 

1.97 

Total concentrate. 

. 79.30 

56.93 

92.61 

Final tailing.. 

. 20.70 

17.39 

7 39 


SCREEN ANALYSES 

Dorr Concentrate Dorr Overflow 





(% solids—8. 

47) 


% by 

% Fe 

% by 

% Fe 


weight 


weight 


+ .371-inch. 

. 35.92 

58.31 



+ 4-mesh. 

. 9.48 

60.90 



+ 8-mesh. 

. 10.82 

58.95 



+ 14-mesh. 

. 7.05 

56.70 



+ 28-mesh. 

. 6.06 

56.40 



-f- 48-mesh. 

. 10.23 

56.55 



65-mesh. 

. 5.11 

54.75 



4-100-mesh. 

. 6.25 

53.02 

1.65 

23.92 

-f200-mesh. 

. 7.00 

51.83 

29.75 

18.22 

—200-mesh. 

. 2.08 

46.12 

68.60 

21.08 

Unsized. 


57.00 

100.00 

20.28 


14 





















Ore No. 475 
Test No. 4 


CONDITIONS OF TEST ON DORR ORE WASHER 

Water rate, 2.6 tons per hr. 

Feed rate, 1.0 tons per hr. 

Rake speed, 30 strokes per min. 



% by 

% Fe 

% Fe by 


weight 


weight 

Feed. 

. 100.00 

48.74 

100.00 

Screen oversize. 

. 26.35 

58.68 

31.72 

Rake concentrate. 

. 50.70 

55.89 

58. 14 

Total coarse concentrate. 

. 77.05 

56.84 

89.86 

Dorr overflow. 

. 22.95 

21.54 

10. 14 

Table concentrate. 

. 1.92 

57.07 

2.25 

Total concentrate. 

. 78.97 

56.85 

92.11 

Final tailing. 

. 21.03 

18.28 

7.89 


SCREEN ANALYSES 

Dorr Concentrate Dorr Overflow 

(% solids = 8.07) 



% by 

% Fe 

% by 

% Fe 


weight 


weight 


+ .371-mch. 

. 34.20 

58.68 



+ 4-mesh. 

. 8.49 

61.11 



+ 8-mesh. 

. 10.03 

58.87 



+ 14-mesh. 

. 7.68 

56.92 



+ 28-mesh. 

. 7.11 

55.50 



+ 48-mesh. 

. 11.58 

55.80 



+ 65-mesh. 

. 5.48 

53.62 



-f 100-mesh. 

. 6.50 

52.43 

2.13 

26.36 

+ 200 mesh. 

. 7.11 

51.38 

28.72 

21 12 

—200-mesh. 

. 1.82 

49.58 

69.15 

21.57 

Unsized. 

. 100.00 

56.84 

100.00 

21.54 


15 





















Ore No. 475 
Test No. 5 


CONDITIONS OF TEST ON DORR ORE WASHER 

Water rate, 5.2 tons per hr. 

Feed rate, J -2 tons per hr. 

Rake speed, 30 strokes per min. 



% by 

% Fe 

% Fe by 


weight 


weight 

Feed. 

. 100.00 

48.74 

100.00 

Screen oversize. 

. 23.80 

58.31 

28.47 

Rake concentrate. 

. 50.71 

56.99 

59.29 

Total coarse concentrate. 

. 74.51 

57.41 

87.76 

Dorr overflow. 

. 25.49 

23.39 

12.24 

Table concentrate. 

. 2 47 

61.26 

3.11 

Total concentrate. 

. 76.98 

57.54 

90.87 

Final tailing. 

. 23.02 

19.32 

9.13 


SCREEN ANALYSES 

Dorr Concentrate Dorr Overflow 

(% solids=2.40) 



% by 

% Fe 

% by 

% Fe 


weight 


weight 


-f .3 71-inch. 

. 31.94 

58.31 



4- 4-mesh. 

. 9.59 

61.41 



+ 8-mesh. 

. 11.31 

59.02 



4- 14-mesh. 

. 9.11 

56.47 



+ 28-mesh. 

. 6.77 

56.10 



4- 48-mesh. 

. 11.36 

56.32 



4- 65-mesh. 

. 5.78 

54.29 

.99 

26.96 

4-100-mesh. 

. 6.57 

53.48 

7.92 

26.14 

fl-200-mesh. 

. 6.17 

56.92 

28.71 

23.52 

— 200-mesh. 

. 1.40 

51.23 

62.38 

22.92 

Unsized. 


57.41 

100.00 

23.39 


16 





















Ore No. 475 
Test No. 6 


CONDITIONS OF TEST ON DORR ORE WASHER 


Water rate, 10.4 tons per hr. 
Feed rate, 1.0 tons per hr. 
Rake speed, 30 strokes per min. 



% by 

%Fe 

% Fe by 


weight 


weight 

Feed. 

. 100.00 

48.74 

100.00 

Screen oversize. 

. 27.44 

58.52 

32.94 

Rake concentrate. 

. 47.69 

56.58 

55.35 

Total coarse concentrate. 

. 75.13 

57.29 

82.30 

Dorr overflow. 

. 24.88 

22.93 

11.70 

Table concentrate. 

. 1.67 

62.31 

2.14 

Total concentrate. 

. 76.80 

57.40 

90.44 

Final tailing. 

. 23.20 

20.09 

9.56 


SCREEN ANALYSES 

Dorr Concentrate Dorr Overflow 

(% solids=2.14) 



% by 

% Fe 

% by 

% Fe 


weight 


weight 


+ .3 71-inch. 

. 36.52 

58.52 



+ 4-mesh. 

. 9.00 

60.52 



+ 8-mesh. 

. 10.89 

58.94 



+ 14-mesh. 

. 7.83 

56.62 



-f- 28-mesh. 

. 6.32 

56.47 



+ 48-mesh. 

. 10.84 

56.62 



+ 65-mesh. 

. 5.41 

54.60 

1.01 

27.11 

-f 100-mesh. 

. 5.96 

53.03 

11.11 

27.34 

+200-mesh. 

. 5.78 

53.25 

23.23 

23.22 

-200-mesh. 

. 1.45 

49.58 

64.65 

22.02 

Unsized... 

. 100.00 

57.29 

100.00 

22.93 


17 





















Ore No. 475 
Test No. 7 


CONDITIONS OF TEST ON DORR ORE WASHER 


Water rate, 5.2 tons per hr. 
Feed rate, 1.0 tons per hr. 
Rake speed. 20 strokes per min. 



% by 

%Fe 

% Fe by 


weight 


weight 

Feed. 

. too .00 

48.74 

100.00 

Screen oversize. 

. 28.21 

58.52 

33.87 

Rake concentrate. 

. 48.97 

55.57 

55.83 

Total coarse concentrate. 

. 77.18 

56.65 

89.70 

Dorr overflow. 

. 22.82 

21.99 

10.30 

Table concentrate. 

. .85 

59.84 

1.05 

Total concentrate. 

. 78.03 

56.68 

90.75 

Final tailing. 

. 21.97 

20.52 

9.25 


SCREEN ANALYSES 

Dorr Concentrate Dorr Overflow 

(% solids=4.33) 



% by 

% Fe 

% by 

% Fe 


weight 


weight 


-f- .371-inch. 

. 36.55 

58.52 



-f- 4-mesh. 

. 8.70 

59.92 



+ 8-mesh. 

. 10.11 

58.72 



+ 14-mesh. 

. 7.25 

57.07 



+ 28-mesh. 

. 7.09 

56.40 



+ 48-mesh. 

. 9.78 

56.40 



+ 65-mesh. 

. 4.99 

54.45 



-f 100-mesh. 

. 5.56 

52.43 

7.84 

26.51 

+200-mesh. 

. 7.67 

48.98 

27.45 

21.20 

-200-mesh. 

. 2.30 

46.29 

64.71 

21.79 

Unsized. 

. 100.00 

56.65 

100.00 

21.99 


18 





















Ore No. 475 
Test No. 8 


CONDITIONS OF TEST ON DORR ORE WASHER 


Water rate, 7.8 tons per hr. 
Feed rate, 3.0 tons per hr. 
Rake speed, 30 strokes per min. 



% by 

%Fe 

% Fe by 


weight 


weight 

Feed. 

. 100.00 

48.74 

100.00 

Screen oversize. 

. 24.78 

58.48 

29.73 

Rake concentrate. 

. 50.14 

56.80 

58.44 

Total coarse concentrate. 

. 74.92 

57.18 

88.17 

Dorr overflow. 

. 25.08 

22.99 

11.83 

Table concentrate. 

. 1.12 

62.27 

1.44 

Total concentrate. 

. 76.05 

57.43 

89.60 

Final tailing. 

. 23.95 

21.15 

10.40 


SCREEN ANALYSES 

Dorr Concentrate Dorr Overflow 

(% solids=9.44) 



% by 

% Fe 

% by 

% Fe 


weight 


weight 


+ .3 71-inch. 

. 33.08 

58.48 



+ 4-mesh. 

. 10.49 

60. 73 



+ 8-mesh. 

. 11.18 

59.58 



+ 14- mesh. 

. 7.50 

57.27 



+ 28 -mesh. 

. 6.90 

56.66 



-f 48-mesh. 

. 10.15 

56.81 



-f 100-mesh. 

. 11.88 

54.04 

5.05 

27.21 

-(-200-mesh. 

. 6.52 

53.51 

34.35 

23.06 

—'200-mesh. 

. 2.30 

47.59 

60.60 

22.60 

Unsized. 

. 100.00 

57.18 

100.00 

22.99 


19 




















Ore No. 475 
Test No. 9 


CONDITIONS OF TEST ON DORR ORE WASHER 


Feed. 

Screen oversize. 

Rake concentrate. 

Total coarse concentrate 

Dorr concentrate. 

Table concentrate. 

Total concentrate. 

Final tailing. 


Water rate, 5.2 tons per hr. 
Feed rate, l. 0 tons per hr. 
Rake speed, 50 strokes per min. 


% by 
weight 

% Fe 

% Fe by 
weight 

100.00 

48.74 

100.00 

23.32 

58.32 

27.90 

48.70 

57.76 

57.72 

72.02 

57.94 

85.62 

27.98 

25.06 

14.38 

2.50 

63.42 

3.26 

74.53 

58.12 

88.88 

25.47 

21.29 

11.12 


SCREEN ANALYSES 

Dorr Concentrate 


Dorr Overflow 
(% solids=5.52) 



% by 

% Fe 

% by 

% Fe 


weight 


weight 


+ .3 71-inch. 

. 32.38 

58.32 



4- 4-mesh. 

. 10.99 

61.19 



+ 8-mesh. 

. 11.82 

59.50 



+ 14-mesh. 

. 8.01 

57.35 



-f- 28-mesh. 

. 9.72 

56.12 



+ 48-mesh. 

. 12.52 

56.58 

4.04 

26.37 

+ 65-mesh. 

. 5.60 

55.20 

1.01 

30.60 

+ 100-mesh. 

. 5.04 

56.73 

4.04 

28.37 

+200-mesh. 

. 3.18 

59.73 

30.30 

28.44 

—200-mesh. 

. .74 

43.51 

60.61 

22.99 

Unsized. 

. 100.00 

57.94 

100.00 

25.06 


20 





















Ore No. 475 
Test No. 10 


CONDITIONS OF TEST ON DORR ORE WASHER 

Water rate, 5.2 tons per hr. 

Feedrate, 1.0 tons per hr. 

Rake speed, 12 strokes per min. 



% by 

%Fe 

% Fe by 

• 

weight 


weight 

Feed. 

. 100.00 

48.74 

100.00 

Screen oversize. 

. 23.62 

58.52 

28.36 

Rake concentrate. 

. 53.56 

55.51 

61.00 

Total coarse concentrate. 

. 77.18 

56.43 

89.36 

Dorr concentrate.. 

. 22.82 

22.72 

10.64 

Table concentrate. 

. .86 

56.51 

1.00 

Total concentrate. 

. 78.04 

56.43 

90.36 

Final tailing. 

. 21.96 

21.40 

9.64 


SCREEN 


+ .3 71-inch 
+ 4-mesh... 
+ 8-mesh.. . 
-f- 14-mesh... 
+ 28-mesh.. . 
+ 48-mesh.. . 
+ 100-mesh... 
+200-mesh.. . 
—200-mesh.. . 
Unsized. 


ANALYSES 

Dorr Concentrate Dorr Overflow 

(% solids = 5.10) 


% by 

% Fe 

% by 

% Fe 

weight 


weight 


30.60 

56.64 



11.37 

60.11 



12.26 

58.53 



7.76 

56.30 



6.77 

55.87 

.68 

25.71 

10.42 

56.30 

4.11 

24.64 

11.19 

53.62 

7.53 

24.71 

6.95 

48.00 

36.97 

21.47 

2.68 

43.59 

50.71 

23.04 

100.00 

55.86 

100.00 

22.72 


21 



>•> 




















Ore No. 475 
Test No. 11 


CONDITIONS OF TEST ON LOG WASHER 

Water rate, 7.7 tons per hr. 

Feed rate, ton per hr. 

Log speed, 18 rev. per min. 



% by 

% Fe 

% Fe by 


weight 


weight 

Feed. 

. 100.00 

48.74 

100.00 

Log concentrate. 

. 70.25 

57.64 

83.09 

Log tailing. 

. 29.75 

27.75 

16.91 

Table concentrate. 

. 4.04 

56.50 

4.68 

Total concentrate. 

. 74.29 

57.58 

87.77 

Total tailing. 

. 25.71 

23.17 

12.23 


SCREEN ANALYSES 

Log Concentrate Log Tailing 



% by 

% Fe 

% by 

% Fe 


weight 


weight 


+ .3 71-inch. 

. 30.82 

57.68 



+ 4-mesh. 

. 18.46 

59.38 



+ 8-mesh. 

. 11.69 

58. 10 



+ 14-mesh. 

. 6.86 

55.74 



+ 28-mesh. 

. 7.51 

55.21 

1.32 

27.70 

-f- 48-mesh. 

. 11.11 

55.93 

4.64 

26.17 

+ 100-mesh. 

. 9.97 

57.74 

19.88 

28.59 

+200-mesh. 

. 2.93 

63.72 

28.38 

31.63 

—200-mesh. 

. .65 

46.00 

45.78 

25.10 

Unsized. 

. 100.00 

57.64 

100.00 

27.75 


< 


< 


22 


















SUMMARY OF TESTS ON DORR ORE WASHER Ore No. 475 










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23 

























































































24 


A MACHINE FOR CONCENTRATING WASH ORES 


DISCUSSION OF RESULTS 

It appears from this test that the sample of ore submitted can 
be treated so as to produce a concentrate assaying from 56.50 to 
58.00 per cent in iron with a recovery of from 77.50 to 72.00 per cent 
by weight. The iron recovery varies from 85.63 to 91.25 per cent. 
These results were secured without the use of tables and without hand 
picking. The presence of a small amount of coarse rock in the coarsest 
size of the ore indicates that hand picking would raise the grade of 
concentrate by possibly J4 of 1 per cent. In order to show a more 
direct comparison of what was accomplished by treating this ore 
under a variety of conditions, hand picking was eliminated. The 
assays made and reported previously indicate that this concentrate 
will carry from 9 to 10 per cent silica and .048 per cent phosphorus. 

In all of these 10 tests made on the Dorr Ore Washer, the 
attempt was made to vary only one condition at a time so as to indi¬ 
cate exactly the effect on the grade of concentrate and the percen¬ 
tage of ore recovered. A standard feed rate of 1 ton per hour was 
used. There was no particular reason for using this as a standard 
feed rate except that it was convenient. No data were at hand to 
indicate the capacity of the Dorr Ore Washer, but by comparison 
with the small log-washing unit, it appeared that this feed rate would 
be a fair basis for comparison. 

A standard water rate of 5.2 tons per hour was used, as this seemed 
to be about the proper quantity of water overflowing from the washer 
to carry away the tailing. This water rate of 5.2 tons per ton of 
ore is a little higher than is used in the standard washing plants. 
In standard practice about 3 tons of water per ton of ore are used. 
From tests with the experimental log-washer unit it appeared that 
small washing machines require a somewhat larger proportion of water 
than the larger machines. In the experimental log-washer nearly 
15 tons of water are used per ton of ore fed. 

A rake speed of 30 strokes per minute was taken as standard as 
this seemed to be the speed at which the majority of Dorr Classi¬ 
fiers making a coarse separation are operated. 

From this standard condition of 1 ton per hoir feed rate, 5.2 tons 
per hour water rate, and 30 strokes per minute rake speed, the feed 
rate, water rate, and rake speed were varied in separate series of 
tests so as to indicate the effect of each. In the first series cf tests 
the rake speed only was varied. 

Variable rake speed .-—It appears from the data that in varying the 
rake speed from 12 strokes per minute to 50 strokes per minute the 


A MACHINE FOR CONCENTRATING WASH ORES 


25 


grade of concentrate made by the Dorr Ore Washer varies from 56.43 
per cent iron to 57.94 per cent iron, with a corresponding recovery 
of concentrate by weight of from 77.18 per cent to 72.02 per cent. 
The iron recovery seems to reach a maximum of 90.04 per cent at 
30 strokes per minute. It is interesting to note that as the speed is 
increased the amount of concentrate recovered by the tables increases 
from .85 per cent to 2.50 per cent, indicating that more of the mineral 
is thrown into the tailing at the higher rake speeds. 

It is of course understood that 50 strokes per minute is consider¬ 
ably above the practical operating speed of a full-size Dorr Classifier. 
This speed of 50 strokes was used in order to secure the required 
amount of agitation to stir the additional amount of low-grade 
material into the tailing. The angle irons which form the rakes on 
this small classifier are only Iff inches deep, and move through 
the body of water without producing a large amount of agitation. 
In the full-size machines, however, the angle irons forming the rakes 
are 4 or 5 inches high, and in moving back and forth through the 
body of water in the tank of the classifier cause a very much greater 
amount of agitation at 30 strokes than is secured in this small classi¬ 
fier at 50 strokes. It is therefore impossible to tell at exactly what 
speed a full-size unit should operate, in order to secure the results 
shown in this table of variable rake speeds. It seems certain, how¬ 
ever, that there will be no difficulty in securing the same amount 
of agitation in a large-size classifier as was secured in this smaller unit. 

Variable water rate .—From the standard water rate of 5.2 tons per 
hour the amount of water was increased to 10.4 tons per hour, and 
decreased to 2.6 tons per hour. The effect of this change in the amount 
of water used was to change the grade of concentrate from 56.84 to 
57.29 per cent iron. This higher grade of concentrate, however, 
was secured at an iron recovery of only 82.30 per cent, which is the 
lowest recorded. It appears that practically no improvement was 
made by increasing the water from 5.2 tons per hour to 10.4 tons 
per hour, but that the loss of iron was considerable. The change in 
the grade of concentrate from 2.6 tons per hour to 5.2 tons per hour 
water rate was approximately .4 of 1 per cent. From this it would 
seem that the most desirable water rate would lie very close to 5.2 
tons of water per ton of ore for this small unit. As was previously 
stated, the small units require more water than the larger units, and 
therefore it is impossible to state the exact amount of water that 
would be required in the full-size washer. 

Variable feed rate .—From the standard condition of 1 ton per hour 
the feed rate was increased to 2 tons per hour, and decreased to 


26 


A MACHINE FOR CONCENTRATING WASH ORES 


ton per hour. This variation changed the grade of concentrate 
produced from 57.00 to 57.41 per cent. At the lower feed rate, how¬ 
ever, the weight of ore recovered was considerably below that recovered 
at the higher feed rate. It is apparent that by changing the feed rate 
and leaving the water rate constant at 5.2 tons per hour, the propor¬ 
tion of water per ton of ore was also changed. With the feed rate 
of y 2 ton per hour, the water used amounted to 10.4 tons of water 
per ton of ore, which is the same as was used in test No. 7. A com¬ 
parison therefore between test No. 7 and test No. 5 shows to some 
extent the effect of varying the feed rate and keeping the amount of 
water per ton of ore constant. The results secured on these two tests 
are practically the same, and in order to carry the comparison further 
another series of tests was made in which the feed rate and water 
rate were both varied, but in all cases 2.6 tons of water were used for 
each ton of ore fed. 

Variable feed and water rate .—A comparison of the results secured 
from this series of tests indicates that as the feed rate is increased the 
grade of concentrate secured increases slightly. This is a condition 
which is often observed in the Dorr Classifiers. The classifying action 
appears to be better when the rakes are well loaded. The exact reason 
for this is somewhat in doubt, but it is probably due to the crowding 
action of the material as it settles. In these tests 2.6 tons of water were 
used per ton of ore fed. This is below what is generally used in the 
standard washing plants. Whether or not this amount of water 
could be further reduced on the full-sized Dorr Ore Washer can not 
be stated. 

Log-washing test .—In the log-washing test the feed rate was only 
Yi a ton per hour and the water rate was 7.7 tons per hour. Just 
what would be the effect of increasing the tonnage fed to the log- 
washer and decreasing the amount of water is not known, but a com¬ 
parison between the results secured on this experimental log-washer 
and the standard log-washers on the Mesabi range has shown in a 
great many cases that the results produced are practically the same. 
The grade of concentrate made by the use of the log-washer was 
57.64 per cent iron, and the recovery by weight was 70.25 per cent. 
This grade of concentrate is as good as was produced on the Dorr 
Ore Washer, but the recovery is considerably lower. When the 
log-washer is followed by tables, however, the recovery and grade 
of concentrate are modified to a point that make them compare favor¬ 
ably with the results secured on the Dorr Ore Washer. In other words 
it appears that the Dorr Ore Washer did practically the same work as 
was accomplished by use of the log-washer and tables together. 


A MACHINE FOR CONCENTRATING WASH ORES 


27 


Application .—As was previously stated, this machine was con¬ 
structed as a result of an investigation having for its object the design of 
a simple and inexpensive plant for concentrating the Mesabi wash ores. 
From the results secured it appears that the machine will produce a 
grade of concentrate comparing very favorably with that secured by 
the log-washer. It further appears from a study of the machine that 
the cost of constructing a plant equipped with this unit would be very 
much below the cost of the standard washing plant. This machine 
contains its own trommel, and it is only necessary to feed the crude 
ore into the hopper of the machine and discharge the coarse and fine 
concentrate together into the cars for shipment. It appears that the 
water required for washing the ore will not be in excess of that re¬ 
quired by the standard washing plant, and that there is a great possi¬ 
bility of less water being necessary. The power required to operate 
the Dorr Ore Washer will be very much less than that required in the 
standard washing plants. It would seem that 30 horse power would 
operate the Dorr Classifier, trommel, feelers, conveyors, and all 
machinery necessary with the exception of the water pumps. It 
would further appear that the steel wear would be very much less 
using the Dorr Ore Washer than in the standard washing plant. 
It is a well-known fact that the classifier itself will operate for many 
years at a very high capacity with practically no replacement cost. 
It then appears that the only item of wear to be considered is the 
trommel. The wear on this trommel will surely be no greater than 
the wear on the trommels in use in the standard washing plants. 
Since the material inside of the trommel in the classifier is partially 
submerged in water, it would seem that the wear on this trommel 
would probably be less than on the trommels now in use. As the 
openings in this trommel are somewhat smaller than are used in the 
standard plant, it is, however, impossible to make any definite state¬ 
ment regarding this factor. 

The capacity of a plant equipped with the Dorr Ore Washer 
has been estimated to be from 1,000 to 1,500 tons per day. It is a 
well-known fact that the classifier itself will easily handle 2,000 
tons of material in 24 hours. The only unknown factor therefore is 
the capacity of the trommel. From all available figures it would 
seem that the trommels should have a capacity of at least 1,500 tons 
per day. Only approximately one third of this material is raked 
out by the classifier, so this tonnage would not be an excessive load 
for the rakes. It further appears from the test data that as the ton¬ 
nage in the classifier increases the results produced improve. It would 
therefore bd an advantage to load this machine as heavily as possible. 


28 


A MACHINE FOR CONCENTRATING WASH ORES 


CONCLUSIONS 

The following conclusions may be drawn from this series of tests: 

1. The Dorr Classifier equipped with a submerged trommel will 
produce practically the same results as are secured in the standard 
log-washing plants now in operation on the Mesabi range. 

2. The cost of constructing a plant equipped with this machine 
would appear to be considerably below the cost of the standard 
washing plants. 

3. The cost of operating a plant with this new equipment should 
be no greater than the cost of operating the log-washing plant. 

4. While it is impossible to make any definite statement regard¬ 
ing the operation of a full-sized Dorr Classifier as a concentrator 
for the Mesabi wash ores, it appears that this .machine would fill a 
definite requirement on the Minnesota iron ranges. 

Respectfully submitted, 

Signed: E. W. Davis, 
Supt. Mines Experiment Station 

Signed: H. H. Wade, 

Metallurgist 


DISCUSSION OF POSSIBLE FLOW SHEETS 

The fact seems fairly well established that the Dorr Ore Washer 
will produce about the same results as are secured in the standard 
washing plants when working on typical wash ores. If considerable 
quantities of free silica exist in the ore coarser than 65 mesh, a log- 
washer will probably produce more satisfactory results than the Dorr 
Ore Washer, as this machine will not overflow as coarse material as the 
logs. However, if there is much coarse silica in the ore the log-washing 
plant does not produce a good concentrate and this siliceous material 
can not be removed without the use of jigs or other concentrating 
machinery. On material in which good ore is associated with a con¬ 
siderable amount of only partially disintegrated silica, the Dorr Ore 
Washer can be made to produce more satisfactory results than are 
secured in the log-washing plant. This may be accomplished by 
using the trommel for the abrasion of the soft material as previously 
suggested. 

In order to be reasonably sure of the results that may be expected 
by the use of the Dorr Ore Washer, actual tests on the ore in ques¬ 
tion should be made. Anyone interested may ship samples of ore to 
the School of Mines Experiment Station at the University of Minne¬ 
sota for testing, and the usefulness of this or other machines in 
connection with any particular concentrating problem may be demon¬ 
strated. Representatives of interested parties can always be present 
at the tests. The sample should weigh about 3 tons and should 
be shipped in sacks weighing about 100 pounds each. The charge 
made for tests covers only the cost of freight, drayage, and the rough 
labor necessary for unloading the ore and moving it about the plant. 
Arrangements should be made with the Superintendent of the Station 
before the sample is shipped. 

In order to show the simplicity of plant construction which may 
be taken advantage of by the use of the new ore-washing machine, 
a few mill flow sheets have been prepared. Flow sheet No. 1 shows 
a possible application to an underground deposit of ordinary wash 
ore. The whole plant is located in the head frame and the skip dumps 
the ore over a grizzly into the hopper above the washing machine. 
A steel apron feeder is used under this hopper in order to maintain 
a uniform rate of feed to the plant. This feeder delivers the ore to 
the trommel of the washer and the concentrate from the machine falls 
onto a conveyor belt located under the classifier tank. The coarse 
material falls on the belt first, thus making hand picking possible. 



I 


FLOW SHEET NO. 

































tN 

o' 

£ 

H 

a 

a 

ffi 

C/3 

£ 

o 

b 
























32 


A MACHINE FOR CONCENTRATING WASH ORES 


A small pocket is provided for the storage of concentrate in order to 
permit shifting cars without closing down the plant. If the head room 
is cramped, however, this pocket may be eliminated as it is entirely 
possible to shut this plant down and start it up again at a moment’s 
notice. One 25 horse-power motor will furnish ample power for the 
operation of the entire plant exclusive of the water pumps and the 
hoist. The plant will have a capacity of 1,000 tons of concentrate 
per day and will require a supply of from 500 to 800 gallons of water 
per minute. It is estimated that this plant, including the head frame, 
could be built at the present time for from $20,000 to $40,000. 

Flow sheet No. 2 shows a possible installation in connection with 
an open-pit mine of good wash ore. The ore is dumped from the pit 
cars over a grizzly and into a bin from which a steel apron feeder 
delivers it, at a constant feed rate, to the incline belt conveyor. 
This conveyor puts the ore directly into the hopper of the washing 
machine and a second incline conveyor carries the concentrate to 
the loading pocket. A 50 horse-power motor would operate this 
plant, and the tonnage handled and water required would be the 
same as given for the previous flow sheet. A plant of this design 
could probably be built for approximately $50,000. 

If the ore available contains a considerable amount of silica 
coarser than 65 mesh and finer than J/£ inch, a flow sheet may be ar¬ 
ranged, similar to No. 1 or No. 2, except that single compartment 
roughing jigs may be added for the purpose of cleaning up the fine con¬ 
centrate from the washer. The jigs may be placed at the upper end 
of the Dorr Ore Washer in such a position that the fine concentrate 
flows to these machines for further cleaning. No crushing or sizing is 
necessary as the product raked out of the classifier is ideal jig feed. 

It has been suggested that a portable washing plant could be 
made by using the Dorr Ore Washer mounted on a flat car and oper¬ 
ated by means of a gasoline engine. This outfit when equipped with 
portable conveyors and supplied with the necessary water might be 
used to concentrate small deposits or stock piles of wash ore. 

Many engineers have visited the Experiment Station, have 
examined the Dorr Ore Washer, and have studied the results of the 
tests. They recognize a possible field of usefulness for this machine 
in Minnesota, and are awaiting with interest the results to be obtained 
from the operation of a full-sized plant. 












